1. Field of the Invention
The present invention relates to a radio transmission method and a radio transmission apparatus applicable to, e.g. a case where a plurality of devices form a local area network (LAN) by transmitting information among various kinds of transmission apparatus by a radio signal.
2. Description of the Related Art
From the past have been proposed various kinds of radio transmission method in which the number of communicating stations forming a radio network is selected to be an arbitrary integer equal to or greater than two, a frame structure common to the radio network being used, a management information transmitting field being provided in a part of the frame and information necessary for managing the network being transmitted and received in the management information transmitting field.
As a first conventional radio transmission method, according to an official gazette of Japanese laid-open patent application No. H11-251992, there is proposed a method in which areas for transmitting station synchronizing signals from all communicating stations forming a network are provided within a predetermined frame period so as to avoid conflict with each other.
As a second conventional radio transmission method, there is conceived a method in which, in that management information transmitting field within a predetermined frame period, a station synchronizing signal transmitting interval during which one communicating station can issue a transmission request is provided and a communicating station having a transmission request, etc. starts transmission in this area as the need arises.
Further, as a third conventional radio transmission method, according to an official gazette of Japanese laid-open patent application No. H11-374728, there is proposed a method in which, in that management information transmitting field, an interval for transmitting station synchronizing information necessary for managing a network can be varied depending on a change in the number of the communicating stations forming the network.
Alternatively, as a fourth conventional radio transmission method, there is conceived a method in which a station synchronizing signal transmission and reception interval during which one communicating station transmits is provided within a predetermined frame period and a communicating station designated by a control station transmits a station synchronizing signal in every frame period.
However, according to the first conventional radio transmission method, there is a disadvantage that, since there are provided in each communicating station the station synchronizing signal transmitting areas of the number corresponding to the number of assumed communicating stations as fixed areas in every frame which arrives periodically, if there are a few communicating stations forming the network, then many useless areas will exist.
According to the second conventional radio transmission method, there is a disadvantage that, when a plurality of communicating stations issue transmission requests at the same time, transmitted signals conflict with each other and so this conventional radio transmission method cannot be applied to a radio transmission in which it is difficult to detect a conflict by simultaneously performing transmission and reception.
According to the third conventional radio transmission method, there is a disadvantage that, because the station synchronizing signal transmitting area increases as the number of the communicating stations forming the network increases, it tends to be difficult to satisfactorily transmit information in the information transmitting field of the latter half of the frame.
According to the fourth conventional radio transmission method, there is a disadvantage that information contained in the station synchronizing signals from all the communicating stations cannot be obtained unless the frame periods corresponding to the number of the communicating stations in operation pass until the transmission of the station synchronizing signals from all the communicating stations forming the network finishes.
Also, according to the fourth conventional radio transmission method, there is a disadvantage that, when the communicating station which is requested to transmit information in the frame period fails to receive down-link control information designating the transmission, the station synchronizing signal from that communicating station cannot be transmitted.